Nevermind- I think I found my answer here:
Permutations and Combinations
Here's my problem: I have forty marbles. 20 of them are black, 20 are white. If I pull them all out and record them, (for example, w,b,w,w,w,b,w,....) how many different combinations are possible?
For cases without identical objects the answer would be (40!), but when they are separated into two identical objects, I don't know the answer.
Thanks for your help!